1. Field of the invention
The present invention relates generally to an image display apparatus, and more particularly to a projection type image display apparatus for displaying a projected image through lenses from a transmissive display device such as liquid crystal panels.
2. Description of the Prior Art
In recent years, projection type display apparatus are widely used to display on large-screen projection televisions, information display systems and the like. FIG. 6 illustrates a typical example of such a projection type of display apparatus 1, hereinafter being referred to as a display apparatus. The display apparatus 1 includes a light source 2 and a reflector lens 3 so that the light from the light source 2 is focused by a condenser lens 4 so as to form an image. A projection lens 7 is disposed adjacent to the image.
A transmissive display device 6 such as a liquid crystal device is disposed between the condenser lens 4 and the projection lens 7. The display device 6 includes layers which independently control the transmission of red, green and blue. The condenser lens 4 allows the light from the source 2 to enter the display device 6, and the pasing light is then projected into an image on a screen 8. The reason why the projection lens 7 is located near the image of the light source 2 is to minimize the diameter of the projection lens 7. This system is called "Kohler's illumination".
Since this system has a structure in which the light through the condenser lens 4 is necessarily focused on the condenser lens 7, the angle of incidence to the display device 6 differs with positions of incidence thereon. In FIG. 6 the angles .theta.1 and .theta.2 have different values. If a plurality of display devices 6R, 6G and 6B are layered as shown in FIG. 6, a "parallax" is likely to occur from one display device to another. As a result, the images represented on the respective display devices 6R, 6G and 6B do not connect to each other on a screen 8, thereby causing chromatic aberration. It is generally explained that this problem is derived from varying projecting magnifications due to different distances between the display devices 6R, 6G and 6B and the projection lens 7.
In order to solve the problems discussed above, there are proposals, among which Japanese Laid-open Patent Publication 60-2916 discloses a method for irradiating a display panel with parallel light rays. This prior art discloses an optical system under which a liquid crystal panel is irradiated with parallel light rays so as to enable a pair of projection lenses to project an image onto the screen. This known method requires a projection lens having a larger diameter than that of the display panel, thereby resulting in an increased production cost and an increased size. In addition, if this optical system has a projection lens constructed with single lenses, a large chromatic aberration is likely to occur. As a result, some suitable means must be provided so as to obviate the possibility of the chromatic aberration, thereby resulting in an increased size and an increased production cost.